Download Weather Elements

Lesson 15A: Weather
Lesson 21: Weather
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AGENDA:
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Causes of Weather
Weather Elements
Basic Weather Phenomena (Fronts, Systems)
Hurricanes/Typhoons
Marine Weather Prediction
Applicable reading: Hobbs WB, App A
Overview
Weather: the state of the Earth’s atmosphere
SPECIFICALLY:
Air Flow:
The circulation of air about the planet
caused by temperature differentials.
Pressure Areas: The relationship between temperature
and pressure and wind.
Fronts:
The transition zone or interface between
two air masses of different densities.
Weather Elements
TEMPERATURE
WINDS
HUMIDITY
PRESSURE
CLOUDS
PRECIPITATION
Temperature
Temperature: the amount heat in the atmosphere.
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Causes:
– The Earth’s daily rotation about its axis
– The Earth’s annual revolution about the sun
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Effects:
– The uneven heating and cooling of the Earth’s
surface results in air flow about the planet.
Wind
Wind: The horizontal movement of the atmosphere
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Causes:
– Temperature differentials
– Coriolis Effect
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Maritime significance:
– Result in areas of High and Low pressure.
Air Flow
Forces that define air flow:
1. Pressure
2. Earth’s Rotation
3. Friction from the surface of the earth
Pressure
Atmospheric Pressure: The weight of the atmosphere.
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Causes:
– Divergence and convergence of air
– Changes in Altitude/Depth
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Maritime significance:
– High/Low pressure systems
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Low (L) - caused by converging winds; rotate counterclockwise
High (H) - caused by diverging winds; rotate clockwise
Low Pressure System
Air Flow
High Pressure System
Air Flow
Weather Fronts
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High and Low pressure systems travel
from the areas where they are created.
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When air masses meet, they “compete”
for dominance.
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The boundary zone between these two
masses is known as a front.
Weather Fronts
Fronts: a zone of transition between air masses
 Cold Front - when a cold air mass displaces a
warm air mass by vigorously forcing it up.
– move fast, 20-35+ kts
– weather deteriorates rapidly
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Warm Front - when a warm air mass displaces a
cold air mass.
– warm air slides over cold air
– move slowly, 19-15 kts
– weather deteriorates gradually
Frontal Passage
Basic Weather
Phenomena
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Clouds
Fog
Tropical storms/hurricanes/typhoons
Heavy Weather
1. Closed Cyclonic - Rotary circulation storms.
2. Noncyclonic - Storms produced by prevailing
winds are identified by their accompanying
winds - predictable.
Closed Cyclonic
1. Tornadoes - Violent, whirling storm of small
diameter that travels across land. Appear as
funnel shaped cloud, with a vortex that may
or may not touch the earth. Winds blow
spirally upwards from 150 - 300 mph.
2. Waterspouts - Similar to tornadoes,
occurring over oceans or inland waters.
Usually less destructive than tornadoes.
Closed Cyclonic
3. Squall - A wind of considerable intensity
caused by atmospheric instability. Comes
up & dies quickly, sometimes accompanied
by thunder, lightning and precipitation.
4. Monsoons - Steady winds somewhat similar
to trade winds. Can reach moderate gale
proportions and are accompanied by heavy
squalls and thunderstorms during the
summer.
Closed Cyclonic
5. Hurricanes - Tropical storm with continuous
winds greater than 75 mph (64 kts).
6. Tropical Storms - Categorized based on
wind speed:
- Tropical Depression: < 34 kts
- Tropical Storm: 34 - 63 kts
- Hurricane: > 63 kts
Noncyclonic
ie: gale - with winds from 34 - 47 mph
storm - with winds of 48 mph or greater.
Weather Elements
(Review)
TEMPERATURE
WINDS
HUMIDITY
PRESSURE
CLOUDS
PRECIPITATION
Clouds
Clouds: condensed water droplets or ice crystals
suspended over the surface of the earth
 Causes of clouds
– Clouds are formed by the cooling of saturated air by the
ocean of land surface beneath.
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Basic Types of Clouds
– Cirrus
– Cumulus
– Stratus
Coastal Fog
Fog: a cloud that “touches” the surface of the earth.
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Causes of clouds/fog
– Clouds are formed by the cooling of saturated air
by the ocean of land surface beneath.
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Prediction of fog
– If the difference between air temperature and
dew point is less than 2°F, fog may result.
Hurricanes/Typhoons
Hurricanes: violent storms with no associated
weather front.
 Causes:
– Storms begin in a low-pressure area, lifting of the air, and
a counter-clockwise inward wind flow.
– Heat released by condensation of water vapor from the
surface below aggravates the process and the storm
builds in intensity.
Review/Summary
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What 3 elements cause weather?
Name 4 of the 6 basic weather elements
What is a front?
Describe the following types of clouds
– Cirrus
– Stratus
– Cumulus
Questions?